The AC joint is where the acromion (a part of the shoulder blade) connects to the clavicle (collar bone) at the top of the shoulder. This joint helps maintain the position of the shoulder and is very important for shoulder control, motion, and strength. The joint is stabilized by a capsule and ligaments, and injury occurs when these structures are damaged. When the capsule and ligaments are injured, the joint can become unstable and painful, and shoulder function can be affected. This type of injury is referred to as an “AC joint sprain” or a “separation.” These injuries typically occur after a sudden fall onto the shoulder. The AC joint is also a common place that arthritis develops, which can become painful. This is usually the result of years of degeneration or “wear and tear” of the joint and is common in weight lifters and laborers.
AC joint injuries
- Pain over the AC joint at the top of the shoulder
- A noticeable bump
- Shoulder tightness and loss of motion
- Pain when lifting the arm up to the side or across the front of the body
If you sustain a fall onto the shoulder and have pain and decreased motion, you should see a doctor. This is also true if you notice a bump or swelling over the AC joint at the top of the shoulder. If you have ongoing pain in this area that doesn’t improve with rest, ice, and over-the-counter pain medication, it should be evaluated.
Sudden AC joint injuries (“sprains” or “separations”) typically occur by one of the following ways:
- A fall onto the shoulder
- Lifting weights or heaving objects
Alternatively, AC joint arthritis typically occurs slowly over time as a result of overuse.
There are a number of factors that increase your risk of an AC joint injury, including:
- Participating in contact sports
- Participating in activities that place you at risk for falling (skiing, mountain biking, ice skating, etc.)
- Working in physically demanding jobs
Nonoperative management with focused physical therapy, rest, and activity modification is considered the primary treatment for the vast majority of AC joint injuries. If the joint is very unstable, surgical repair may be indicated to improve stability of the AC joint, relieve pain, and optimize shoulder function. For patients with AC joint arthritis, an injection may also be considered. For some patients with severe AC joint arthritis that does not respond to nonoperative treatment, surgery may be an option. This is typically performed in a minimally invasive fashion with a relatively quick recovery.